Measurement of total testosterone in women: comparison of a direct radioimmunoassay versus radioimmunoassay after organic solvent extraction and celite column partition chromatography

Objective: To evaluate the clinical usefulness for the measurement of testosterone (T) values in the "low" female range with a direct radioimmunoassay (RIA) for total T by comparing total T values measured by this assay with values determined by conventional RIA after organic solvent extraction/column chromatography. Design: Cross-sectional study. Setting: Victoria, Australia. Patient(s): Two hundred fifty-nine healthy women, aged 18-75 years, recruited from the community. Intervention(s): Fasting serum samples were obtained and stored at -80 degrees C. Main Outcome Measure(s): Total T measurement. Total T was measured by the direct RIA method using antibody-coated tubes and iodine-labeled T tracer. For comparison, total T levels were also measured using the conventional RIA method after organic solvent (ethyl acetate:hexane [3:2]) extraction and celite column partition chromatography before RIA. Result(S): The mean T level by direct RIA was 0.76 nmol/L (median, 0.70; SD, 0.54; minimum, 0.10; maximum, 3.2). The mean difference between the two measurements (direct RIA-conventional RIA) was -0.28 (SD, 0.3). The direct RIA value was 63% (95% confidence interval, 26%-155%) of the conventional RIA estimate. For the classification of values at the lower end of the range, there was very good agreement beyond chance (kappa 0.68-0.74) for values in approximately the lowest 10th-40th percentiles. Conclusion(s): The direct RIA is a clinically useful assay for the study of the issue of "low" T within the female population.